1. Field of the Invention
The present invention relates to a method for measuring micro displacements, particularly, to a method for measuring micro displacements adopting photonic crystals as sensors.
2. Description of Related Art
In precision machinery, such as a Micro-Electro-Mechanical Systems (MEMS), relative displacement between parts need to be precisely measured.
Since photonic crystals have a unique effect of a photonic bandgap, micro displacement sensors based on photonic crystals are widely used in the measurement of micro displacements, e.g., measurement sensitivity of the high sensitivity displacement sensor based on photonic crystal waveguide, can be higher than 1.6a−1 within the measurement range from 0 to 1.5a (“a” is a lattice constant of the photonic crystal); the sensors, based on the photon tunneling effect and Fano interference, can achieve transmittance contrast of 20 dB when the relative displacement changes 1% of optical wavelength, and the micro-displacement sensor, based on the defect resonance cavity of photonic crystal, can achieve a measurement sensitivity of 1.15a−1 within the measurement range from −0.55a to 0.60a.
However, during the process of the above-mentioned micro-displacement measurement, it is difficult to have a greater dynamic range, due to the small measurable displacement range of micro-displacement sensors, and thereby, the micro-displacement sensors cannot usually measure displacement over two lattice constants.
What is needed, therefore, is a method for measuring micro displacements, adopting a photonic crystal as a micro-displacement sensor, with a large dynamic range and with an ability to measure displacement over two lattice constants.